The present invention relates to a rough rolling mill train in a hot rolling mill equipment which effects thickness reduction hot rolling of a flat slab to produce a thin plate and, more particularly, to a rough rolling mill train which is suitable to decrease temperature lowering of a rolling material (rough bar) during rough rolling and improve the productivity thereof thereby.
In a hot rolling mill equipment which produces a thin plate through thickness-reduction hot rolling of a slab, a rough rolling mill train is for rolling of a material from a slab to a rough bar. The rough bar is sent to a finish rolling mill train to be further rolled for reduction of thickness, whereby a hot strip (thin plate) is produced. Usually, the thickness of the slab is 200-280 mm, the width is 700-2,200 mm and the length is 6-13 m.
Hitherto, such a slab would be rolled to reduce the thickness through rolling of 6 passes in total (usual pass numbers) from the slab of thickness 200-280 mm to a rough bar of thickness 20-40 mm, using a rough rolling mill train of arrangement as illustrated in FIG. 5a, 5b, 5c, 5d. The rough rolling mill train illustrated in FIG. 5a is a semi-continuous rough rolling mill train which has one rolling mill RSB effecting one pass one way rolling and one reversing rolling mill R11 effecting 5-pass reversing rolling. A rough rolling mill train illustrated in FIG. 5b is a full-continuous rough rolling mill train for effecting 6-pass rolling by 6 rolling mills R21-R26 each effecting one way rolling. A rough rolling mill train illustrated in FIG. 5c is a three quarters type rough rolling mill train which has, at the outlet side of one rolling mill R31 effecting one pass one way rolling, one reversing rolling mill R32 effecting 3-pass reversing rolling and two rolling mills R33, R34 each effecting one way rolling. Further, a rough rolling mill train illustrated in FIG. 5d is a close couple type rough rolling mill provided with one reversing rolling mill R42 effecting 3-pass reversing rolling at the outlet side of one rolling mill R41 effecting one-pass one way rolling, and one close couple rolling mill R40 having 2 rolling roll assemblies R43, R44 arranged close to each other within one housing to roll a rolling material in turn.
However, in the above-mentioned rough rolling mill trains, since a distance between rolling mill stands is long, about 40 m, the equipment length in any case of FIGS. 5a to 5b becomes longer than 100 m, and since a rolling material is developed on tables between rolling mill stands as thickness reduction rolling progresses, a hot-rolling material grows cold on the tables and a large temperature drop such as more than 100.degree. C. occurs in some cases.
Further, in a case of FIG. 5a, a rolling material is stopped of travelling at each pass, rolling of reversing pass is effected after a screw down amount of rolling rolls, etc. at the rolling mill is reset, so that a lot of time is required and the productivity is lowered remarkably. Particularly, the rolling material is elongated to be very long around the final pass, so that reversing rolling under such a condition requires much longer time. Further, in cases of FIGS. 5c and 5d, also, reversing rolling is effected, so that a lot of time is required for rolling and the productivity is feared to decrease.
On the contrary, an example of a rough rolling mill train, which is suited for improving the temperature lowering and the productivity decrease, is disclosed in JP A 4-367305. This prior art is a reversing type rough rolling mill train which is provided with two thickness reduction rolling mills (twin mills), in each of which two pairs of work rolls (2-high rolling roll assemblies) are arranged in series in an adjacent relation with each other within one housing. According to this system, since the number of times that the rolling material is developed on tables is decreased, it is possible to reduce remarkably a temperature drop. Further, in the prior art, since a rolling material is rolled in a tandem condition in one direction without reversing rolling, the productivity lowering as mentioned above is avoided.
Further, JP A 5-161902 discloses a rolling mill equipment in which two double rolling mills are arranged in tandem close to each other with a distance of 6 m between rolling mill stands. According to this example, it is possible to improve the temperature drop as mentioned above.
In the rough rolling mill trains illustrated in FIGS. 5a to 5d, since the above-mentioned temperature drop occurs and a lot of time is required for rolling, there is some fear of decrease in productivity.
Further, in the prior art disclosed in the JP A 4-367305, a rolling material bestrides a plurality of rolling mills arranged tandem during rolling and it is rolled continuously. The term bestrides when used in this context refers to the rolling material essentially being worked upon by two adjacent tandem rolling mills as described and illustrated in JP A 4-367305. In that system, a rolling speed is large at a final outlet side of the rolling mill train but small at an inlet side of the rolling mill train. For example, supposing that the thickness of a slab is 240 mm at an inlet side of a rough rolling mill train, the thickness of a rough bar is 30 mm at an outlet side and the rough bar is rolled at a usual speed of 200 m/min, a speed of the slab at the inlet side becomes slow, about 25 m/min. Therefore, a contact time between the rolling rolls and the rolling material becomes long, the rolling material is cooled, temperature of the rolling rolls are raised, and there was the possibility that the life of the rolling rolls be reduced remarkably.